Verification of the isotopic composition of precipitation simulated by a regional isotope circulation model over Japan

The isotopic composition (O-18 and H-2) of precipitation simulated by a regional isotope circulation model with a horizontal resolution of 10, 30 and 50km was compared with observations at 56 sites over Japan in 2013. All simulations produced reasonable spatio-temporal variations in O-18 in precipitation over Japan, except in January. In January, simulated O-18 values in precipitation were higher than observed values on the Pacific side of Japan, especially during an explosively developing extratropical cyclone event. This caused a parameterisation of precipitation formulation about the large fraction of precipitated water to liquid detrained water in the lower troposphere. As a result, most water vapour that transported from the Sea of Japan precipitated on the Sea of Japan side. The isotopic composition of precipitation was a useful verification tool for the parameterisation of precipitation formulation as well as large-scale moisture transport processes in the regional isotope circulation model.